The U.S. Food and Drug Administration (FDA) is probing an uptick in reports of serious and life-threatening blood clots and severe narrowing of blood vessels in patients taking the leukemia chemotherapy drug Iclusig (ponatinib).

Clinical trial data and post-market adverse event reports show that patients taking Iclusig have suffered deadly heart attacks, worsening coronary artery disease, stroke, narrowing of the large arteries of the brain, severe narrowing of blood vessels in the extremities, and the need for urgent surgical procedures to restore blood flow.

Iclusig is prescribed for patients with chronic phase, accelerated phase, or blast phase chronic myeloid leukemia (CML) or Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) who are no longer benefitting from previous treatment or who did not tolerate previous treatment.

Iclusig was approved by the FDA in December 2012. Prior to its approval, 8 percent of patients treated with the drug during clinical trials suffered serious arterial blood clots. The FDA indicated this risk in the Boxed Warning and Warnings and Precautions sections. In the most recent clinical trials, however, at least 20 percent of participants treated with Iclusig developed blood clots or narrowing of blood vessels.

The FDA recommends in a Drug Safety Communication released Friday that healthcare professionals should consider for each patient whether the benefits of Iclusig outweigh the risks. The agency also warned patients taking Iclusig to seek medical attention should they experience heart attack symptoms, such as chest pain or pressure, pain in their arms, back, neck or jaw, or shortness of breath; or symptoms of a stroke, such as numbness or weakness on one side of the body, trouble talking, severe headache, or dizziness.